Optical unit and projection type projector apparatus using the same

ABSTRACT

By making the beam polarization state in a cross prism having a dichroic function for an incident beam on a reflection type liquid crystal panel the same as that for a reflected ON beam, a small-sized, low cost projection type projector apparatus is provided. A Faraday rotator having a Faraday rotation angle of 45 degrees is disposed on an optical path between a PBS and a cross prism. A half-wave plate having such a polarization axis as to rotate a polarization angle of linearly polarized light by 45 or 135 degrees is disposed on an optical immediately before or behind the Faraday rotator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/356,000, filed Jan. 31, 2003 and titled “OpticalUnit and Projection Type Projector Apparatus Using the Same,” which isrelated to and claims priority from Japanese Patent Application2002-048938, filed Feb. 26, 2002, and is herein incorporated byreference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to a projection type projector apparatususing a reflection type liquid crystal panel, such as a so-called liquidcrystal projector or projection type television using forwardprojection.

Liquid crystal projectors for business use have widely spread.Furthermore, as a substitute for a conventional image display apparatusof such a scheme that an image displayed on a cathode-ray tube isprojected onto a screen, development of a projection type televisionusing liquid crystal display elements has been conducted.

Liquid crystal panels are classified into transmission type crystalpanels and reflection type crystal panels, according to their types. Inthe reflection type liquid crystal panels, a beam passes through aliquid crystal layer twice and consequently the thickness of the liquidcrystal layer can be reduced by that amount as compared with thetransmission type liquid crystal panels. As a result, the reflectiontype liquid crystal panels are excellent in fast response performance,and consequently they are suitable for dynamic picture display, i.e.,application of projection type television.

On the other hand, in the transmission type liquid crystal panels, theso-called ON state and OFF state are generated by a shutter operation ofthe liquid crystal itself. In the case of the reflection type liquidcrystal panels, both a beam in the ON state and a beam flux in the OFFstate are reflected on the same optical path, and consequently apolarization beam splitter (hereafter abbreviated to PBS) for conductingbeam separation on the basis of a difference in polarization statebecomes an indispensable component.

The PBS action on a reflection type liquid crystal panel will now bedescribed by using FIG. 12. In FIG. 12, reference numeral 1 denotes aPBS, 5 a cross prism for performing dichroic action, and 6 a reflectiontype liquid crystal panel. In FIG. 12, if light aligned with S-polarizedlight in an illumination optical system or only S-polarized light in theillumination optical system is input to the PBS 1, then the S-polarizedlight is reflected by a PBS plane of the PBS 1 and input to the crossprism 5. White light incident on the cross prism 5 is separated intothree colors R, G and B by the dichroic action. The R, G and B coloredbeams are input to the reflection type liquid crystal panels 6respectively corresponding to R, G and B. If each pixel is in the ONstate in FIG. 12, then each of the beams input to the reflection typeliquid crystal panels 6 respectively corresponding to R, G and B isconverted in polarization state from S-polarized light to P-polarizedlight, and reflected. On the other hand, if each pixel is in the OFFstate, then each beam is reflected while it is still S-polarized light.Beams of R, G and B input to the cross prism 5 again are subjected tocolor synthesis by the cross prism 5. As for beams incident on the PBS1, each of beams in the ON state is a P-polarized beam and consequentlyit is transmitted through the PBS 1 this time, input to a projectionlens (not illustrated), and projected. On the other hand, each of beamsin the OFF state remains an S-polarized beam and consequently it isreflected by the PBS 1 again, and returned to its original light sourceside.

SUMMARY OF THE INVENTION

In a conventional reflection type liquid crystal display apparatus, itis necessary in the reflection type liquid crystal panel 6, whichreflects both the ON beam and the OFF beam, to convert the polarizationstate of the ON beam from the S-polarized light to the P-polarizedlight, as described above. This holds true even if the S-polarized lightand the P-polarized light are replaced with each other.

As for the polarization state of light that passes through the crossprism 5, therefore, for example, it is S-polarized light before it isreflected by the reflection type liquid crystal panel 6 and it isP-polarized light after it has been reflected by the reflection typeliquid crystal panel 6. In the case where the cross prism 5 is used withS-polarized light and P-polarized light for the same wavelength, thewavelength characteristic in S-polarized light differs from that inP-polarized light. As a result, fine spectral transmission factorperformance cannot be obtained. For example, desired image light of eachcolor output from each reflection type liquid crystal panel 6 is notoutput from the cross prism 5.

Over against this problem, there has been proposed a scheme ofseparating one color from the white color by using a dichroic prism or adichroic filter, converting a polarization state of one of two colors,and conducting color separation and synthesis by using the PBS. In thisscheme, a total of three PBSs and one dichroic prism or dichroic filterare needed. Thus, this scheme is disadvantageous in size, weight andcost.

An object of the present invention is to make a polarization state of abeam incident on a reflection type liquid crystal panel the same as apolarized state of a reflected ON beam supplied from the reflection typeliquid crystal panel in a configuration using a cross prism having adichroic function and the reflection type liquid crystal panel, andthereby provide a small-sized, light-weighted, low cost illuminationapparatus, and a projection type projector apparatus using theillumination apparatus.

In an optical unit including a light source, a polarization beamsplitter, a color separation and synthesis unit having a dichroicfunction, and reflection type liquid crystal panels, a Faraday rotatoris disposed on an optical path between the polarization beam splitterand the cross prism, and a polarization direction of a beam that passesthrough the Faraday rotator is rotated by a predetermined angle.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a color separation and synthesissection in a first embodiment of the present invention;

FIGS. 2A and 2B are diagrams of a polarization axis of a colorseparation and synthesis section in a first embodiment of the presentinvention;

FIG. 3 is a diagram showing a general configuration of an optical systemof a projection type projector apparatus using a color separation andsynthesis section in a first embodiment of the present invention;

FIG. 4 is a configuration diagram of a color separation and synthesissection having a sheet polarizer on each of optical paths between across prism and reflection type liquid crystal panels in a firstembodiment of the present invention;

FIG. 5 is a configuration diagram of a color separation and synthesissection in a second embodiment of the present invention;

FIGS. 6A and 6B are diagrams of a polarization axis of a colorseparation and synthesis section in a second embodiment of the presentinvention;

FIG. 7 is a configuration diagram of a color separation and synthesissection in a third embodiment of the present invention using an obliqueview;

FIG. 8 is a configuration diagram of a color separation and synthesissection in a third embodiment of the present invention;

FIGS. 9A and 9B are diagrams of a polarization axis of a colorseparation and synthesis section in a third embodiment of the presentinvention;

FIG. 10 is a diagram showing relations among polarization axes of apolarization conversion element, a PBS, and a cross prism in a thirdembodiment of the present invention;

FIGS. 11A and 11B are diagrams showing a function of a Faraday rotatorused in the present invention; and

FIG. 12 is a configuration diagram showing polarization states of acolor separation and synthesis section in a reflection type liquidcrystal panel using a cross prism.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereafter, embodiments of the present invention will be described withreference to FIGS. 1 to 11B.

FIGS. 1, 2A, 2B and 3 are diagrams of a first embodiment of the presentinvention. FIG. 1 is a basic configuration diagram of a color separationand synthesis section included in a projection type projector apparatus.FIGS. 2A and 2B are diagrams showing details of polarization states of abeam. FIG. 3 is a diagram showing a general configuration of an opticalsystem of a projection type projector apparatus using a color separationand synthesis section shown in FIG. 1.

In FIG. 1, reference numeral 1 denotes a PBS having a function ofreflecting S-polarized light and transmitting P-polarized light andmaking it go straight on. Numeral 2 denotes a Faraday rotator includinga garnet crystal plate. Numeral 3 denotes a half-wave plate having apolarization axis for rotating incident linearly polarized light by 45degrees. Numeral 4 denotes a magnet for providing the Faraday rotatorwith a constant direction of magnetic field application, 5 a cross prismhaving a dichroic function, and 6 a reflection type liquid crystalpanel.

First, the function of the Faraday rotator 2 will now be described withreference to FIGS. 11A and 11B.

FIGS. 11A and 11B are diagrams showing how a polarization angle ofcertain linearly polarized light is changed by the Faraday rotator. Acombination of a polarizer A, a Faraday rotator, a polarizer B, and amagnet shown in FIGS. 11A and 11B is an isolator. The isolator is anapparatus for removing harmful return reflected light caused at aconnection portion of optical connection. According to the Faradayeffect, such a property that the polarized wave direction of lightrotates (optical rotary power) is obtained. Unlike the ordinary opticalrotary power (natural optical rotary power), however, reversing thetraveling direction of light does not restore the original state, butfurther rotates the polarized wave direction in the Faraday effect.Hereafter, this will be described concretely with reference to FIG. 1.

In the case of forward traveling light, linearly polarized light inputto the polarizer A in the same polarization direction as the polarizer Ais rotated in polarization direction by 45 degrees by the function ofthe Faraday rotator, and passed through the polarizer B having adirection of 45 degrees. In the case of backward traveling light,linearly polarized light reflected and returned is passed through thepolarizer B and thereafter rotated by 45 degrees in the same directionagain by the Faraday rotator, and consequently it cannot pass throughthe polarizer A. In other words, harmful reflected and returned lightcan be removed.

In the half-wave plate as well, it is possible to rotate thepolarization direction of the linearly polarized light by 45 degrees.Supposing that a half-wave plate for rotating linearly polarized lightin the same direction as the Faraday rotator is disposed, the half-waveplate rotates the linearly polarized light that is backward travelinglight, in a direction opposite to the original rotation direction.Resultant light is passed through the polarizer A.

In FIGS. 11A and 11B, a garnet crystal plate is used as the Faradayrotator with such a plate thickness and an applied magnetic field thatthe Faraday rotation angle becomes 45 degrees.

In FIG. 1, an incident beam aligned in polarization state withS-polarized light ((i)) is input to the PBS 1. The S-polarized light isreflected by a PBS plane of the PBS 1 toward the cross prism 5, andinput to the Faraday rotator 2. Linearly polarized light ((ii)) obtainedby rotating the S-polarized light by 45 degrees in the Faraday rotator 2is then further rotated by 45 degrees in the half-wave plate 3 to becomeP-polarized light ((iii)). White light with P-polarization incident onthe cross prism 5 is separated into three colors R, G and B by thedichroic function of the cross prism 5, and R, G and B beams arereflected respectively by the reflection type liquid crystal panels 6corresponding to respective colors. Each reflection type liquid crystalpanel 6 is driven by a drive circuit, which is not illustrated, on thebasis of an input video signal. Each reflection type liquid crystalpanel 6 is provided with a function of reflecting an ON beam whilekeeping the polarization state at P-polarized light, and converting thepolarization state from P-polarized light to S-polarized light for anOFF beam. This function becomes opposite to the case of the reflectiontype liquid crystal panel 12. However, it can be coped with by applyingwhite-black inversion to drive of the reflection type liquid crystalpanels 6 shown in FIG. 12.

Subsequently, beams reflected by the reflection type liquid crystalpanels 6 are subjected to color synthesis in the cross prism 5, andinput to the half-wave plate 3. In the case of an ON beam, P-polarizedlight ((iv)) is input to the half-wave plate 3, and consequently itbecomes linearly polarized light ((v)) in the direction of 45 degreesthat is the same as the original direction, and it is input to theFaraday rotator 2. In the Faraday rotator 2, the beam is rotated by 45degrees in the same direction again, and resultant P-polarized light((vi)) is transmitted through the PBS 1. On the other hand, in the caseof an OFF beam, S-polarized light ((iv)) is input to the half-wave plate3, and consequently it becomes linearly polarized light ((v)) in thedirection of 45 degrees that is opposite to the original direction (adirection perpendicular to the direction of the case of the ON beam at90 degrees), and it is input to the Faraday rotator 2. In the Faradayrotator 2, the beam is rotated by 45 degrees in the same directionagain, and S-polarized light ((vi)) is restored and consequently it isreflected by the PBS 1.

The polarization directions of (i), (ii), (iii), (iv), (v) and (vi)shown in FIG. 1 will now be described in detail with reference to FIGS.2A and 2B. In FIGS. 2A and 2B, polarization axes of an incidence systemare indicated by coordinates seen from an incidence side, andpolarization axes of a reflection system are indicated by coordinatesseen from an emission side. In other words, the coordinate system of theincidence system becomes the same as that of the emission system. As fordefinition of the S-polarized light and P-polarized light, polarizedlight polarized in parallel to a plane of incidence defined by a planeformed by a direction of propagation of incidence light and a normalline of a boundary plane is P-polarized light, and polarized lightpolarized at right angles to the plane of incidence is S-polarizedlight. In FIGS. 2A and 2B, S-polarized light and P-polarized light areindicated by arrows of polarization directions of the S-polarized lightand P-polarized light, respectively.

The incident S-polarized light ((i)) is rotated by 45 degreescounterclockwise ((ii)) by the Faraday rotator 2. Subsequently, thelinearly polarized light in a leftward rising direction of 45 degreesshown in FIG. 2A is folded back around a polarization axis of thehalf-wave plate 3 having an angle of 22.5 degrees clockwise with respectto a horizontal axis (X-axis) shown in FIG. 2A to become the P-polarizedlight ((iii)). Subsequently, the P-polarized light ((iv)) that is an ONbeam reflected by the reflection type liquid crystal panels 6 is foldedback around the polarization axis of the half-wave plate 3 having theangle of 22.5 degrees clockwise with respect to the horizontal axis(X-axis) shown in FIG. 2A to become the linearly polarized light ((v))in a leftward rising direction of 45 degrees as shown in FIG. 2B.Finally, in the Faraday rotator 2, the linearly polarized light isrotated to the same direction as the original direction, i.e., by 45degrees counterclockwise to become the P-polarized light ((vi)).

Although not illustrated, the S-polarized light that is an OFF beamreflected by the reflection type liquid crystal panels 6 is folded backaround the polarization axis of the half-wave plate 3 having the angleof 22.5 degrees clockwise with respect to the horizontal axis (X-axis)shown in FIG. 2A to become linearly polarized light in a rightwardrising direction of 45 degrees in FIG. 2B, which is opposite to theoriginal state. Finally, in the Faraday rotator 2, the linearlypolarized light is rotated to the same direction as the originaldirection, i.e., by 45 degrees counterclockwise to become theS-polarized light. Typically, the cross prism 5 is designed givingpriority to the priority states (P-polarized light) of the incident beamand the reflected ON beam. Therefore, a part of the reflected OFF beamdoes not return to the PBS 1. For example, a part of the reflected OFFbeam arrives at opposed reflection type liquid crystal panels 6. FIG. 4is a configuration diagram of a configuration obtained by disposing asheet polarizer 7, which passes only the polarization direction of theincident beam and the reflected ON beam, on each of optical pathsbetween the cross prism 5 and the reflection type liquid crystal panels6 in the configuration shown in FIG. 1. Even in the case where thespectral transmittance performance of the cross dichroic prism 5 is notfine, it becomes possible in FIG. 4 to easily absorb reflected OFF beamsdiffering in polarization state with the sheet polarizer, by disposingthe sheet polarizer 7, which passes only the polarization direction ofthe incident beam and the reflected ON beam, on each of the opticalpaths between the cross prism 5 and the reflection type liquid crystalpanels 6. On the other hand, in the case of the configuration as shownin FIG. 12, the polarization state of the incident beam differs from thepolarization state of the reflected ON beam, and consequently it is notpossible to dispose a sheet polarizer on each of optical paths betweenthe cross prism 5 and the reflection type liquid crystal panels 6.

The rotation angle of the polarization axis effected by the half-waveplate 3 may not be 45 degrees but may be 135 degrees. If in this casethe polarization axis of the half-wave plate 3 shown in FIGS. 2A and 2Bis rotated by 90 degrees, then it is possible to further rotate thepolarization direction of linearly polarized light by twice as great as90 degrees, i.e., 180 degrees. It is a matter of course that anequivalent effect can be obtained, for example, even if two quarter-waveplates having the same polarization axis are provided.

Instead of the configuration in which the beam aligned with S-polarizedlight is first input to the PBS 1, a configuration in which a beamaligned with P-polarized light is input to the PBS 1 may also beadopted. In that case, the angle of the polarization axis of thehalf-wave plate 3 should be changed according to the state of polarizedlight incident on the cross prism 5. In the same way, the beam firstincident on the the cross prism 5 may not be P-polarized light, but maybe S-polarized light. In that case as well, the angle of thepolarization axis of the half-wave plate 3 should be changed.

As for the rotation angle caused by the Faraday rotator 2, it is onlynecessary in the same way that S-polarized light and P-polarized lightare interchanged after passage in two round trips, and consequently therotation angle should be 45 degrees or 135 degrees, i.e., half of 90degrees or half of 270 degrees. This case should be also coped optimallywith the polarization angle of the half-wave plate 3 corresponding tothe rotation angle.

The general configuration of the optical system of the projection typeprojector apparatus using the color separation and synthesis sectionwill now be described with reference to FIG. 3.

In FIG. 3, reference numeral 11 denotes a light source, 12 a concavemirror, 13 an integrator, 14 a polarization conversion element, 15 animage forming lens, 16 a reflecting mirror, 17 a field lens, and 18 aprojection lens. Reference numerals 1 to 6 denote the same components asthose shown in FIG. 1. By forming the concave mirror 12 in aparaboloidal form and disposing the light source 11 in a position of afocal point of the paraboloid, light from the light source is reflectedby the concave mirror 12 to become a beam parallel to the optical axis.By the integrator 13 formed of two sets of multi-lens arrays eachincluding lenses arranged in a two-dimensional form, light from thelight source is converted to a plurality of secondary light sourceimages. Natural light is separated into P-polarized light andS-polarized light by the polarization conversion element 14 disposedimmediately after the integrator 13, and then the polarization state isaligned with S-polarized state. The secondary light source images thathave become S-polarized light are led to the reflection type liquidcrystal panels 6 by the image forming lens 15 and the field lens 17. Tobe concrete, light quantity distributions of respective lenses on thefirst multi-lens array plane are superposed on planes of the reflectiontype liquid crystal panels 6. In FIG. 3, two lenses, i.e., the imageforming lens 15 and the field lens 17 are used, and the image forminglens 15 bears mainly the image forming function whereas the field lens17 bears mainly the function of making the principal beam incident onthe reflection type liquid crystal panels 6 telecentric. However, thenumber of lenses may be three, or conversely it is also possible thatone lens bear the functions. Furthermore, in FIG. 3, the mirror 16 isdisposed on the way to bend the optical path and the whole apparatus canbe made compact. The mirror 16 may be provided with a function oftransmitting ultraviolet rays and infrared rays harmful to thereflection type liquid crystal panels 6 and reflecting only a visibleray. As for ultraviolet rays, it is also effective to further dispose anultraviolet ray absorbing filter on an optical path in the middle.

In the first embodiment, it is supposed that the PBS 1 has such acharacteristic to white light as to reflect S-polarized light andtransmit P-polarized light. However, it is also possible to design thecharacteristics of the PBS 1 so as to reflect S-polarized light andtransmit P-polarized light for the G beam and transmit P-polarized lightand reflect S-polarized light for the R beam and B beam, and change onlythe polarization states of a specific color in the rotator beforeincidence on the PBS 1 and thereby first input the G beam to the PBS 1as S-polarized light and the R beam and the B beam to the PBS 1 as theP-polarized light. In this case, polarization states of respectivecolors of the cross prism 5 can be divided into P-polarized light forthe G beam and S-polarized light for the R beam and B beam at the timeof incidence and ON reflection, and consequently the performance of thecross prism 5 can be improved.

A second embodiment of the present invention will now be described withreference to FIGS. 5 and 6. FIG. 5 is a basic configuration diagram of acolor separation and synthesis section of a projection type projectorapparatus. FIGS. 6A and 6B are diagrams showing details of beampolarization states.

In FIG. 5, an incident beam aligned in polarization state withS-polarized light ((i)) is input to the PBS 1. The S-polarized light isreflected by the PBS plane of the PBS 1 toward the cross prism 5, andinput to the half-wave plate 3. Linearly polarized light ((ii)) obtainedby rotating the linearly polarized light by 45 degrees in the half-waveplate 3 is then further rotated by 45 degrees in the Faraday rotator 2to become P-polarized light ((iii)). White light with P-polarizationincident on the cross prism 5 is separated into three colors R, G and Bby the dichroic function of the cross prism 5, and R, G and B beams arereflected respectively by the reflection type liquid crystal panels 6corresponding to respective colors. Each reflection type liquid crystalpanel 6 is provided with a function of reflecting an ON beam whilekeeping the polarization state at P-polarized light, and converting thepolarization state from P-polarized light to S-polarized light for anOFF beam.

Subsequently, beams reflected by the reflection type liquid crystalpanels 6 are subjected to color synthesis in the cross prism 5, andinput to the Faraday rotator 2. In the case of an ON beam, P-polarizedlight ((iv)) is input to the Faraday rotator 2 and rotated by 45 degreesin the same direction again, and consequently it becomes linearlypolarized light ((v)) in the direction of 45 degrees that is opposite tothe original direction, and it is input to the half-wave plate 3. Thelinearly polarized light is folded back around a polarization axis ofthe half-wave plate 3. Resultant P-polarized light ((vi)) is transmittedthrough the PBS 1. On the other hand, in the case of an OFF beam,S-polarized light ((iv)) is input to the Faraday rotator 2 and rotatedby 45 degrees in the same direction again, and consequently it becomeslinearly polarized light in the direction of 45 degrees that is the sameas the original direction (a direction perpendicular to the direction ofthe case of the ON beam at 90 degrees), and it is input to the half-waveplate 3. In the half-wave plate 3, therefore, the beam is restored tothe S-polarized light ((vi)), which is the same as the originalpolarized light, and consequently it is reflected by the PBS 1.

The polarization directions of (i), (ii), (iii), (iv), (v) and (vi)shown in FIG. 5 will now be described in detail with reference to FIGS.6A and 6B. In FIGS. 6A and 6B, polarization axes of an incidence systemare indicated by coordinates seen from an incidence side, andpolarization axes of a reflection system are indicated by coordinatesseen from an emission side. In other words, the coordinate system of theincidence system becomes the same as that of the emission system. Theincident S-polarized light ((i)) is folded back around the polarizationaxis of the half-wave plate 3 having an angle of 22.5 degreescounterclockwise with respect to a vertical axis (Y-axis) shown in FIG.6A to become the linearly polarized light ((ii)) in a leftward risingdirection of 45 degrees as shown in FIG. 6A. Subsequently, the linearlypolarized light is rotated by 45 degrees counterclockwise by the Faradayrotator 2 to become the P-polarized light ((iii)). The Faraday rotator 2rotates linearly polarized light in the same direction as the originalstate, i.e., by 45 degrees counterclockwise. Therefore, the P-polarizedlight ((iv)) that is an ON beam reflected by the reflection type liquidcrystal panels 6 is rotated to become linearly polarized light ((v)) ina rightward rising direction of 45 degrees as shown in FIG. 6B. Thelinearly polarized light ((v)) is input to the half-wave plate 3 andfolded back around the polarization axis of the half-wave plate 3 havingthe angle of 22.5 degrees counterclockwise with respect to the verticalaxis (Y-axis) shown in FIG. 6A to become the P-polarized light ((vi))

Although not illustrated, the S-polarized light that is an OFF beamreflected by the reflection type liquid crystal panels 6 is rotated bythe Faraday rotator 2, which rotates linearly polarized light in thesame direction as the original state, i.e., by 45 degreescounterclockwise, to become linearly polarized light in a leftwardrising direction of 45 degrees in FIG. 6B. The resultant linearlypolarized light is folded back around the polarization axis of thehalf-wave plate 3 having the angle of 22.5 degrees counterclockwise withrespect to the vertical axis (Y-axis) shown in FIG. 6A to becomeS-polarized light.

A third embodiment of the present invention will now be described withreference to FIGS. 7 to 10. FIGS. 7 and 8 are basic configurationdiagrams of a color separation and synthesis section of a projectiontype projector apparatus. FIGS. 9A and 9B are diagrams showing detailsof beam polarization states. FIG. 10 is a diagram showing an action of ahalf-wave plate in a third embodiment of the present invention.

A great difference of the third embodiment from the first embodimentshown in FIG. 1 and the second embodiment shown in FIG. 4 is in that thePBS 1 is rotated by 45 degrees as shown in FIG. 7.

S-polarized light for the PBS 1 is inputted to the PBS 1, reflected bythe PBS plane, and input toward the cross prism 5.

In FIG. 8, an incident beam aligned in polarization state for the PBS 1with S-polarized light ((i)) is input to the PBS 1. The S-polarizedlight is reflected by the PBS plane of the PBS 1 toward the cross prism5. However, the normal line direction of the cross prism 5 and thenormal line direction of the PBS 1 are related to each other by arotation of 45 degrees. Therefore, S-polarized light for the PBS 1becomes linearly polarized light in the direction of 45 degrees for thecross prism 5. The linearly polarized light in the direction of 45degrees is rotated by 45 degrees in the Faraday rotator 2 to becomeP-polarized light ((iii)). White light with P-polarization incident onthe cross prism 5 is separated into three colors R, G and B by thedichroic function of the cross prism 5, and R, G and B beams arereflected respectively by the reflection type liquid crystal panels 6corresponding to respective colors. Each reflection type liquid crystalpanel 6 is provided with a function of reflecting an ON beam whilekeeping the polarization state at P-polarized light, and converting thepolarization state from P-polarized light to S-polarized light for anOFF beam.

Subsequently, beams reflected by the reflection type liquid crystalpanels 6 are subjected to color synthesis in the cross prism 5, andinput to the Faraday rotator 2. In the case of an ON beam, P-polarizedlight ((iv)) is input to the Faraday rotator 2 and rotated by 45 degreesin the same direction again, and consequently it becomes linearlypolarized light ((v)) in the direction of 45 degrees that is opposite tothe original direction. The linearly polarized light in the direction of45 degrees that is opposite to the original direction becomesP-polarized light ((vi)) for the PBS 1, and it is transmitted throughthe PBS 1. On the other hand, in the case of an OFF beam, S-polarizedlight ((iv)) is input to the Faraday rotator 2 and rotated by 45 degreesin the same direction again, and consequently it becomes linearlypolarized light in the direction of 45 degrees that is the same as theincident beam. For the PBS 1, the linearly polarized light is restoredto S-polarized light ((vi)), which is the same as the original polarizedlight, and consequently it is reflected by the PBS 1.

The polarization directions of (i), (ii), (iii), (iv), (v) and (vi)shown in FIG. 8 will now be described in detail with reference to FIGS.9A and 9B. In FIGS. 9A and 9B, polarization axes of an incidence systemare indicated by coordinates seen from an incidence side, andpolarization axes of a reflection system are indicated by coordinatesseen from an emission side. In other words, the coordinate system of theincidence system becomes the same as that of the emission system. Sincethe normal line direction of the PBS 1 is displaced from the normal linedirection of the cross prism 5 by 45 degrees, the S-polarized light((i)) incident on the PBS 1 becomes linearly polarized light ((ii)) in aleftward rising direction of 45 degrees as shown in FIG. 9A for thecross prism 5. Subsequently, the linearly polarized light is rotated by45 degrees counterclockwise by the Faraday rotator 2 to become theP-polarized light ((iii)). Subsequently, the P-polarized light ((iv))that is an ON beam reflected by the reflection type liquid crystalpanels 6 is rotated by the Faraday rotator 2, which rotates linearlypolarized light in the same direction as the original state, i.e., by 45degrees counterclockwise, to become linearly polarized light ((v)) in arightward rising direction of 45 degrees in FIG. 9B. In the same way,since the normal line direction of the PBS 1 is displaced from thenormal line direction of the cross prism 5 by 45 degrees, P-polarizedlight ((vi)) for the PBS 1 is obtained.

Although not illustrated, the S-polarized light that is an OFF beamreflected by the reflection type liquid crystal panels 6 is rotated bythe Faraday rotator 2, which rotates linearly polarized light in thesame direction as the original state, i.e., by 45 degreescounterclockwise, to become linearly polarized light in a leftwardrising direction of 45 degrees. In the same way, since the normal linedirection of the PBS 1 is displaced from the normal line direction ofthe cross prism 5 by 45 degrees, S-polarized light for the PBS 1 isobtained.

S-polarized light for the PBS 1 will now be described with reference toFIG. 10. FIG. 10 is a diagram showing relations among the polarizationdirection in the polarization conversion element 14, the polarizationdirection in the PBS 1, and the polarization direction in the crossprism 5.

In order to superpose light quantity distributions of respective lenssurfaces included in the integrator 13 on the reflection type liquidcrystal panels 6, optical mapping relations between the polarizationconversion element 14 and the reflection type liquid crystal panels 6must be maintained. Therefore, the polarization direction of thepolarization conversion element 14 and the polarization direction of thecross prism 5 also become the same. On the other hand, since there is adifference of 45 degrees between the polarization direction of the crossprism 5 and the polarization direction of the PBS 1, there is also adifference of 45 degrees between the polarization direction of thepolarization conversion element 14 and the polarization direction of thePBS 1. In the third embodiment of the present invention, therefore, itis necessary to dispose a half-wave plate for rotating the polarizationdirection of linearly polarized light by 45 degrees and generatingS-polarized light for the PBS 1, on the optical path between thepolarization conversion element 14 and the PBS 1.

According to the present invention, the polarization state beforeincidence on reflection type liquid crystal panels and the polarizationstate of the ON beam after the reflection effected by the reflectiontype liquid crystal panels are made the same in a configuration using across prism having a dichroic function, as heretofore described. As aresult, a small-sized, lightweight, low cost illumination apparatus anda projection type projector apparatus using such an illuminationapparatus can be obtained.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An optical unit comprising: a light source; a polarization beamsplitter; a color separation and synthesis unit having a dichroicfunction; reflection type liquid crystal panels; wherein said opticalunit further includes a first optical element in an optical path betweensaid beam splitter and said color separation and synthesis unit forrotating polarization direction of light flux to a first predeterminedangle toward traveling direction of the light; and a second opticalelement for rotating said polarization direction of said light flux to asecond predetermined angle independent of said traveling direction ofthe light.
 2. An optical unit according to claim 1; wherein said secondoptical element comprises a Faraday rotator and said color separationand synthesis unit comprises a cross dichroic prism.
 3. An optical unitaccording to claim 1; wherein said first optical element comprises apolarization direction rotating optical element having a functionequivalent to a half-wave plate or quarter-wave plates, and said secondoptical element is a Faraday rotator.
 4. An optical unit according toclaim 1; wherein said first optical element is disposed in an opticalpath between said second optical element and said color separationsynthesis unit.
 5. An optical unit according to claim 1; wherein saidsecond optical element is disposed in an optical path between said firstoptical element and said color separation synthesis unit.
 6. An opticalunit according to claim 1; wherein said first and second predeterminedangle are substantially the same angle.
 7. An optical unit according toclaim 6; wherein said first and second predetermined angle issubstantially 45 degrees or 135 degrees.
 8. A projection type displayapparatus comprising: a light source; a polarization beam splitter; acolor separation and synthesis unit having a dichroic function;reflection type liquid crystal panels; a first optical element in anoptical path between said beam splitter and said color separation andsynthesis unit for rotating polarization direction of light flux to afirst predetermined angle toward traveling direction of the light; asecond optical element for rotating said polarization direction of saidlight flux to a second predetermined angle independent of said travelingdirection of the light; a drive circuit for driving said reflection typeliquid crystal panel in accordance with an image signal; and aprojection lens for extending projecting optical image from saidreflection type liquid crystal panel inputted through said polarizingbeam splitter.
 9. An optical unit according to claim 8; wherein saidfirst optical element comprises a polarization direction rotatingoptical element having a function equivalent to a half-wave plate orquarter-wave plates, and said second optical element is a Faradayrotator.
 10. An optical unit according to claim 8; wherein said firstand second predetermined angle are substantially the same angle.
 11. Anoptical unit according to claim 6; wherein said first and secondpredetermined angle is substantially 45 degrees or 135 degrees.